The present invention relates to a device for controlling the speed of an engine, and, more particularly, to a device for controlling the engine speed with an improved response.
As is well known in the art, an engine mounted on a motor vehicle has a carburetor. The carburetor has a throttle valve with a throttle shaft which rotates in response to depression of an accelerator pedal to control the amount of air fuel mixture supplied to the engine.
The carburetor is provided with an accelerating pump for increasing fuel supply to the engine when the accelerator pedal is depressed to a large extent. The accelerating pump has an adjusting rod. The adjusting rod is coupled to the throttle shaft through a lever mechanism, as disclosed in Japanese Utility Model Laid Open Nos. 62-56752, 62-110558 and 62-116154. When the throttle shaft is rotated, the rotation is transmitted to the adjusting rod through the lever mechanism to displace the rod longitudinally, and the rod causes a piston to slide for increasing the amount of fuel supplied to the engine by means of the accelerating pump.
However, a relatively large torque is required for rotating the throttle shaft because of the mechanical connection of the accelerating pump to the throttle valve.
On the other hand, the engines of recent motor vehicles are installed with an engine speed control device. The engine speed control device is typically in the form of a governor device having governor weights which swing or expand radially outwardly for maintaining a predetermined vehicle speed, to cause a governor lever to swing so as to rotate the throttle shaft in a direction toward a close position of the throttle valve. Consequently, the vehicle speed does not exceed 105 Km/h, for example, in the case of a small motor vehicle.
As mentioned above, a relatively large torque is required for rotating the throttle shaft in the known devices, wherefore there occurs a delay in the response of the engine speed control device together with deviation of the maximum vehicle speed at which the throttle shaft is rotated in a direction toward the close position of the throttle valve.